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There are many ways to define The Environment. Some of the more prominent of these are described here: a- The Gaseous, Liquid, and Solid Environments The environment can be considered as existing in one of three forms— gaseous, liquid, or solid. Each of these is subject to pollution, and people interact with all of them. Particulates and gases are often released into the atmosphere, sewage and liquid wastes are discharged into water, and solid wastes, particularly plastics and toxic chemicals, are disposed of on land. 2

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b- The Chemical, Biological, Physical, and Socioeconomic Environments Another perspective considers the environment in terms of the four avenues or mechanisms by which various factors affect people’s health. 1. Chemical constituents and contaminants include toxic wastes and pesticides in the general environment, chemicals used in the home and in industrial operations, and preservatives used in foods. 2. Biological contaminants include various disease organisms that may be present in food and water, those that can be transmitted by insects and animals, and those that can be transmitted by person-to-person contact. 3

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3. Physical factors that influence health and well-being range from injuries and deaths caused by accidents to excessive noise, heat, and cold and to the harmful effects of ionizing and non-ionizing radiation. 4. Socioeconomic factors, though perhaps more difficult to measure and evaluate, significantly affect people’s lives and health. Statistics demonstrate compelling relationships between morbidity and mortality and socioeconomic status. People who live in economically depressed neighborhoods are less healthy than those who live in more affluent areas. 4

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C- The Inner Versus Outer Environment From the standpoint of the human body, there are two environments: the one within the body and the one outside it. Separating them are three principal protective barriers: the skin, which protects the body from contaminants outside the body; the gastrointestinal (GI) tract, which protects the inner body from contaminants that have been ingested; and the membranes within the lungs, which protect the inner body from contaminants that have been inhaled. 5

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Although they may provide protection, each of these barriers is vulnerable under certain conditions. Contaminants can penetrate to the inner body through the skin by dissolving the layer of wax generated by the sebaceous glands. The GI tract, which has by far the largest surface area of any of the three barriers, is particularly vulnerable to compounds that are soluble and can be readily absorbed and taken into the body cells. Fortunately, the body has mechanisms that can protect the GI tract: un wanted material can be vomited via the mouth or rapidly excreted through the bowels (as in the case of diarrhea). 6

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Airborne materials in the respirable size range may be deposited in the lungs and, if they are soluble, may be absorbed. Mechanisms for protecting the lungs range from simple coughing to cleansing by macrophages that engulf and promote the removal of foreign materials. Unless an environmental contaminant penetrates one of the three barriers, it will not gain access to the inner body, and even if a contaminant is successful in gaining access, the body still has mechanisms for controlling and/or removing it. For example, materials that enter the circulatory system can be detoxified in the liver or excreted through the kidneys. 7

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Environmental Health: In its broadest sense, environmental health is the segment of public health that is concerned with assessing, understanding, and controlling the impacts of people on their environment and the impacts of the environment on them. The environmental health can also be defined as the discipline that focuses on the interrelationships between people and their environment “Air, water, soil, food,..etc.”, promotes human health and well-being, and fosters a safe and healthful environment. 8